Failure of a tantalum lined tee induced by hydrogen embrittlement

Abstract

A lined tee leaked a high temperature mixture of HCI gas and steam from the inner tantalum liner into the external carbon pipe. The main causes of failure have been proposed based on several analysis methods, including macroscopic examination, metallographic inspections, chemical composition analysis, hardness test, scanning electron microscopy analysis and energy dispersive spectrometry test. On the basis of experimental analyses, computational fluid dynamics simulations were employed to explore the flow fields of HCI gas and steam in pipelines. It was found that the failure region of the tantalum liner was coincidence with the mixture zone of two media. The root cause of failure was the formation of liquid hydrochloric acid during the start-up of equipment, causing that hydrogen ions in liquid hydrochloric acid penetrated into tantalum, resulting in hydrogen embrittlement cracks. Meanwhile, pitting corrosion was caused in mixing areas. Adjusting the structure of tee pipe from T-type to Y-type was put forward to prevent equipment failure.